Motor

ABSTRACT

A motor comprising two or more rotors ( 20, 30 ) rotated by means of a common power supply ( 6 ), each rotor ( 20, 30 ) having a plurality of poles ( 22, 32 ) and being associated with a stator ( 16, 26 ) having a plurality of poles ( 18, 28 ), wherein the arrangement of rotor poles ( 22, 32 ) and stator poles ( 18, 28 ) is different for each rotor 920, 30) so that the rotors ( 20, 30 ) rotate at different speeds when the common power supply ( 6 ) is applied.

FIELD OF THE INVENTION

The invention relates to a motor.

BACKGROUND OF THE INVENTION

Many developments have been made over the years to motors, in particularto those motors which are used in domestic household appliances.However, it is generally believed that the trend of improvements inrelation to universal motors is nearing its end. It is therefore anobject of the present invention to provide a motor which is suitable forproviding the appropriate power to various parts of a domestic householdappliance and which also has scope for improvement beyond the potentialof known universal motors.

Domestic household appliances such as vacuum cleaners very often includea universal motor adapted to drive the fan used to create the suction bymeans of which air is drawn into the vacuum cleaner. When the vacuumcleaner is an upright cleaner, a brush bar is usually mounted rotatablyin the dirty air inlet located in the cleaner head. The brush bar isrotated by means of a drive belt extending between the motor and thebrush bar. There are many disadvantages of this arrangement, not leastof which is the vulnerability of the drive belt itself. Otherdisadvantages include the fact that, in most cases, the drive beltengages with a portion of the outer surface of the brush bar which meansthat brush bristles cannot be located in that area. It is alsoadvantageous to have some sort of mechanism for preventing the brush barfrom rotating against a carpet to be cleaned if, for any reason, themotor is left running whilst the vacuum cleaner remains stationary, forexample, whilst carrying out above-floor cleaning.

In a cylinder cleaner, the dirty air inlet is situated at the end of ahose, hence a drive belt to the main vacuum motor is impractical, anddriving the brush bar directly by a secondary universal motor haspractical difficulties. Pneumatically powered “turbo” brushes have beenproposed, but they are normally inefficient and reduce the power wattsavailable for the pickup of dirt and dust by the cleaner head.

It is therefore an object of the invention to provide a motor suitablefor use in a vacuum cleaner having a driven brush bar but which reducesor eliminates the problems identified above.

SUMMARY OF THE INVENTION

The invention is to a motor. In particular, the invention is to a motorhaving at least two rotors.

The provision of at least two rotors in the motor has been identified asan economical and compact way of driving two separate features of ahousehold appliance such as a vacuum cleaner at different speeds. Makinguse of a common stator and the same winding or windings or a commonpower supply to drive two separate rotors is clearly advantageous in anenvironment in which consumers demand small, lightweight appliances.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of alternative embodiments of the invention will now bedescribed by way of example with reference to the accompanying drawingsin which:

FIG. 1 is a schematic view of a primary and secondary motor arrangement;

FIGS. 2a-2 d are sectional and cross-sectional views of the brush barincorporating the secondary motor of FIG. 1;

FIGS. 3a-3 d are sectional and cross-sectional views of a second brushbar incorporating a secondary motor such as shown in FIG. 1;

FIGS. 4a-4 g are schematic cross-sectional views of various alternativemotors in accordance with the present invention;

FIGS. 5a and 5 b are schematic cross-sectional views of alternativemotor arrangements in accordance with the invention;

FIG. 6 is a schematic cross-sectional view of a motor in accordance withthe present invention; and

FIG. 7 is a still further cross-sectional view of a motor in accordancewith the present invention; and

FIG. 8 is a schematic sectional view of a further motor in accordancewith the invention; and

FIG. 9 shows an arrangement in which a motor and generator are coupledtogether.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a primary 4/2 two-phase switched reluctance motor 2, asecondary 24/16 two-phase switched reluctance motor 4 and a power supplycircuit which is connected to the primary motor 2. Other types ofswitched reluctance motor, (e.g. single phase, three phase, four phase,etc) could be used for either motor, if desired. The arrangement shownis perceived as being particularly suitable for driving the fan andbrush bar of a vacuum cleaner, although this is by no means the onlyapplication envisaged.

In common with known switched reluctance motors, the primary motor 2comprises a stator 16 with four salient poles 18 a-18 d. Opposed poles18 a and 18 b each support a like armature winding +A,−A which form afirst phase. Opposed poles 18 c and 18 d accommodate respective likearmature windings +B,−B which represent a second phase. A rotor 20 isrotatably mounted upon an axis 21 within the stator 16 and comprisesopposed poles 22. The rotor 20 is formed from steel laminated in theaxial direction.

Power is supplied to the motor 2 from a mains supply 6 which isrectified by a bridge rectifier 8. A capacitor 10 is provided forsmoothing the bridge output. Each of the armature winding pairings A,Bis fed via a respective asymmetric half bridge 12,14. Each half bridge12,14 relates to a respective one of the two phases. In this regard,half bridge 12 supplies the A windings and half bridge 14 supplies the Bwindings.

For continuous operation, current is applied to each of the statorphases in turn at a rate which is dependent on and determined by thevariation of the rotor position with time. The timing of the asymmetrichalf bridges 12,14 is determined by reference to the rotor positions ofthe primary and/or secondary motors by means of either optical or Halleffect sensors or any other suitable means.

The primary reluctance motor 2 also includes two additional windingpairs: C and D. One winding of winding pair C is accommodated on each ofsalient poles 18 a and 18 b. One winding of the winding pair D isaccommodated on each of the salient poles 18 c and 18 d.

The respective pairings of windings A and C on the one hand and B and Don the other each operate in the manner of a transformer. The currentinduced in winding pairs C and D by winding pairs A and B is supplied tothe secondary reluctance motor 4. For convenience of assembly within thebrush bar of the vacuum cleaner, this motor is structurally the inverseof the primary motor 2. That is to say, the rotor 30 is situatedradially outside the stator 26, which is located upon a fixed axis 34.The radially inner surface of the brush bar 36 is fitted directly uponthe radially outer surface of the rotor 30 and secured in place bysplines 37.

Closer reference to FIG. 1 will reveal that the stator 26 comprisessixteen poles 32. The rotor 30 comprises twenty-four radially inwardlydirected poles 28. The poles 32 situated upon the stator 26 are arrangedin pairs, with each pair being surrounded by a respective winding. Thewindings themselves are paired circumferentially and then these pairs ofwindings are in turn paired with a similar pair of windings situated onthe radially opposite side of the stator. For example, poles 32 a and 32b are provided with a D winding. Circumferentially adjacent poles 32 cand 32 d are provided with a second D winding. Radially opposite, poles32 e-32 h are arranged in a similar fashion. The spacing between thepoles 32 a-32 h is such as to enable their simultaneous radialcorrespondence with rotor poles 28, as shown in the figure. However, thepoles associated with the D windings are radially off-set from the coilsassociated with the C windings, such that radial correspondence with therotor poles cannot be achieved by the poles associated with the C coilsat the same time as the poles associated with the D coils. Hence atwo-phase structure results.

The number of poles provided in the secondary switched reluctance motor2 ensures smooth rotation of the brush bar 36.

The power supply to the primary reluctance motor 4 is typically switchedat a frequency of the order of 1.25 kHz per phase, (if a 4/4 singlephase switched reluctance motor were used as the primary a switchingfrequency of about 2.5 kHz would be comparable). The secondaryreluctance motor can be switched at the same, high frequency (or reducedratio by disconnecting the secondary windings from the number of poles).As a consequence of this magnitude of frequency, there is no need toprovide for a high level of flux build-up in the coil armature of theprimary motor (or an intermediate transformer, if the voltage is steppeddown outside the primary motor). Because the voltage to the secondarymotor 4 is stepped-down and isolated from the voltage of the primarymotor 2, the supply of power to the secondary motor is very safe. Infact, the supply is so safe that the power can be fed via the hose tothe suction head of a cylinder vacuum cleaner without a risk ofcompromising safety.

Supplying power to the primary motor 2 via the power supply circuitcauses the primary rotor 22 to rotate within the stator 16. The currentflowing within the coils A,B induces current in coils C,D which in turncauses the secondary rotor 30 to rotate about the secondary stator 36.The number of poles present on each stator 16,36 and rotor 22,30determines the relative speeds of rotation; in this example, thesecondary rotor 30 will rotate at one twelfth of the speed of theprimary rotor 22.

Switches 38 are provided in order to enable the electrical connection tothe windings C,D to be interrupted. The switches can be operatedmanually or triggered automatically in response to the conditions of thedevice in which the motor is situated. For example, it may be desirableto switch off the brush bar of a vacuum cleaner under some circumstancesand operation of the switches 38 can achieve this. The switches can bemade to open in the event that the handle of the vacuum cleaner is putinto the upright position by means of simple electronic circuitry whichwill be readily available to a skilled reader. The switches can also beoperated intermittently, for example during start-up of the brush bar,so that the rotation of the brush bar can be brought up to speed in acontrolled and reliable manner.

By using a switched reluctance motor as the secondary motor 4,significant advantages arise. Due to the lack of commutating brushes, nocarbon powder is generated by brush wear. Furthermore, the motor has arelatively long life and its speed is not limited by the need tomaintain a reasonable brush life. Use of a switched reluctance motor asthe primary motor enables a switched reluctance motor to be used as thesecondary motor with relative ease.

FIGS. 2a-2 d show the secondary motor 2 of FIG. 1, situated within avacuum cleaner brush bar 36, in more detail. FIG. 2a is a section. Views2 b-2 d are cross-sections taken along lines I to III in FIG. 2a,respectively. Referring to FIG. 2a, it will be seen that the brush bar36 and rotor 28 are together mounted by means of bearings 40 upon theshaft 34 that supports the stator 26. The shaft 34 is mounted at eachend to a housing 42 of the vacuum cleaner. From cross sectional FIG. 2c,it will be seen that the shaft 34 includes four axial grooves 42situated at circumferential intervals (eg 90°). Each groove 42accommodates a wire for supplying current from the primary motor 2 tothe secondary motor 4.

FIGS. 3a-3 d show a variation of the arrangement of FIG. 2. FIG. 3a is asection and FIGS. 3b to 3 d are cross-sections taken along lines I toIII in FIG. 3a, respectively. In this set-up, the shaft 34 is hollow andthe wires for supplying current to the windings of the secondary motorrun inside the shaft, as can clearly be seen from cross sectional FIG.3c.

Although the above arrangements have a greater number of poles in thesecondary motor than in the primary motor, this is not necessary. Theprimary motor can have an equal or greater number of poles relative tothe secondary motor if circumstances require it. For example on awashing machine, a primary motor used as a direct drive could operate atabout 0-2000 rpm and drive a secondary motor for a high-speed water pumpoperating at 0-10,000 rpm. In such a case, it would be appropriate forthe primary motor to have a greater number of poles than the secondarymotor. In the case of the example mentioned, the primary motor will havea pole arrangement capable of driving the secondary motor at five timesthe speed of the primary motor.

FIG. 4 illustrates various embodiments of the invention, in each ofwhich one or more windings are used to drive more than one rotor of asingle motor. FIG. 4a illustrates an embodiment having similarities tothe arrangements illustrated in FIGS. 1 to 3. The motor 500 has a stator502 carrying a winding A and twenty four external poles 504. Rotatablymounted radially outwardly of the stator 502 is an external rotor 506,also carrying twenty four poles 508. A plurality of splines 510 arearranged between the external rotor 506 and the interior surface of abrush bar cylinder 512 of a vacuum cleaner. This arrangement can be usedto cause rotation of the brush bar 512 in the same way as is describedin relation to the earlier figures.

The main difference between the motor illustrated in FIG. 4a and thepreviously illustrated motors is the provision of four internal poles514 on the stator 502. Radially inwardly of the stator 502 is mounted asecond, inner rotor 516 having four equispaced poles 518. The innerrotor 516 is rotatably mounted about a central axle 520.

It will be appreciated that, simultaneously with the rotation of theexternal rotor 506 when power is supplied to the winding A, the innerrotor 516 will also rotate. However, the speed of rotation of the innerrotor 516 will be six times the speed of rotation of the external rotor526 due to the difference in the number poles provided on each rotor andthe associated stator.

It will also be appreciated that this principle can be applied to manyalternative arrangements and very many alternative variations arepossible. FIGS. 4b, c, d, e and f each show, schematically, differentarrangements of a single switched reluctance motor having a commonwinding or set of windings driving two separate rotors. In each case,the number of poles carried by each rotor is different. It will beappreciated that the number of poles on each rotor can be varied atwill. FIG. 4g illustrates schematically a two-phase switched reluctancemotor having two windings instead of one and also driving two separaterotors. One advantage of driving two separate rotors by means of onewinding or set of windings is that the volume occupied by the motor willbe reduced and the associated mass will therefore also be reduced.

The rotors of a motor in accordance with the invention can either rotateuni-, contra- or multi-directionally.

In the case of a switched reluctance motor, the initial direction ofrotation is usually determined by the initial position of the rotorpole(s) relative to the stator pole(s) and/or the phase switchingsequence(s) when a current pulse is applied to the winding(s).

If one considers the motoFIG. 4, it is possible to obtain either uni- orcontra-directional rotation by locating the rotors at suitablerespective orientations relative to the stator prior to the applicationof a current pulse. FIGS. 5a and 5 b show a motor in which magnets 550are provided for parking the rotors when the driving current isterminated, so that the rotors will be in a suitable position forcontra-directional rotation when a current is next applied. In thisregard, FIG. 5a shows a motor with different speed outputs at an initialparking position prior to the application of a driving current. FIG. 5bshows the direction of rotation of the respective rotors after thewinding is excited. It will be seen from the figure that the two rotorsrotate in respectively opposite directions. It will be seen that themagnets are strategically positioned in order to align each of the polesof the rotors to be closer to one particular pole than an adjacent pole.Therefore, when the coil is excited, each rotor pole moves towards thatclosest stator pole, thereby determining the direction of rotation.Naturally, a mechanism could be provided for adjusting the position ofthe magnets, so as to change the direction of rotation of a particularmotor.

An alternative for multi-phase switched reluctance motors having morethan one rotor is to arrange the phase sequences to be such that theyproduce either uni- or contra-directional rotation in the rotors. It isalso possible to control the direction of the rotation by providingasymmetrical air gaps between the rotor and stator poles.

The above motor arrangements allow contra-directional rotating elementsto be provided without a prohibitive increase in cost or mechanicalcomplexity. The motor arrangements can also provide significantadditional advantages as follows. First, net angular momentum can becancelled or reduced. This leads to the minimization ofacceleration/retardation reaction torques on both the motor and/or theappliance or product to which it is fitted. Furthermore, net gyroscopiceffects can be cancelled or reduced. This leads to a minimisation ofgyroscopic forces on the motor and/or the appliance or product whensubject to general movement. Such motor arrangements also enable areduction of acoustic and mechanical vibrations through various methodsincluding superposition cancellation.

A motor having contra-directional rotors, such as described above, canprovide significant asignificant advantages when used in a vacuumcleaner for rotating motorised dual or multiple cyclones. Morespecifically, the motor can be used to drive the impellers inside theinner and outer bins directly. Further, if desired, the air flowsthrough the inner and outer cyclones can be connected inseries—resulting in a potential load matching between the motor'soutputs and thus a simplification and reduction of the power electronicsand/or mechanical complexity.

In the case of switched reluctance motors, the switching times ofprimary and/or additional windings can be controlled using informationfrom position sensor(s) on the primary and/or additional rotor(s). Ifdesired, the positional information of the rotors can be combined (e.g.via a microprocessor, combinational logic or physical construction ofthe sensor(s)) to give the desired operating characteristics for themotor and/or the product/appliance they are used within or incombination with. This allows for a potential simplification of thepower electronics circuitry and thus a potential reduction in theoverall cost, size and weight of the product/appliance.

FIGS. 6 and 7 show variations of the winding structure for a dual outputsingle phase motor, such as shown in FIG. 4a, for example. In each ofFIGS. 6 and 7, the stator 502 is provided with two sets of windings. Inthis regard, a first winding 550 is wound around the radially inwardlydirected poles 518 and a second winding 560 is wound around the radiallyoutwardly directed poles 504.

FIG. 7 shows a broadly similar arrangement to FIG. 6, however there issome radial overlap between the radially inner windings 550 and theradially outer windings 560. This arrangement enables significantreductions in size for a given number of winding turns.

In vacuum cleaner applications, it is possible to provide more than oneimpeller to draw the air through the cleaner. Typically, and inaccordance with the embodiment shown in FIG. 8, a first impeller 570 canbe arranged upstream of the bag (not shown) which separates the dirt anddust from the airflow whilst a second impeller 572 can be arrangeddownstream thereof. The first impeller 570 can be rotated more slowlythan the second impeller 572 but can have a larger size to accommodatethe passage of larger dust particles. The second impeller 572 can bemade relatively smaller because it only sees finer dust particles. Thisfacilitates an elevated operating speed which further improves theperformance of the vacuum cleaner. Further, the ratio of the speeds ofthe rotors can be configured to compensate for the ratios of fan/rotorinertias thus allowing for reduced or net zero gyroscopic forces. Athird motor output could be provided to rotate a brush bar.

Looking at FIG. 8 in more detail, the motor arrangement comprises acentral mechanical support 574 supporting an axially central stator 576provided with laminated poles 590. The poles 590 are provided withwindings 578. A pair of axially aligned rotors 580, 581 are provided onrespective axial sides of the stator 576. The impellers 570, 572 areprovided on the axial sides of the rotors 580, 581 remote from thesupport 574. The impellers 570, 572 and rotors 580, 581 are mounted upona central shaft 582 which is integrally formed with the support 574.Parking magnets 584 are provided for locating the poles 586 of eachrotor 580, 581 closer to poles which are respectively oncircumferentially opposite sides of the mid-point between any givenadjacent pairing of stator poles 590. This has the effect of causing therotors 580, 581 to rotate in opposite directions when the windings 578are excited. To ensure that the impellers 570, 572 draw air fromopposite sides of the motor arrangement, each impeller 570, 572 hasvanes 588 which are oriented in the opposite direction to those of theother impeller. Air can thus be drawn from the dirty air inlet of thevacuum cleaner by the impeller 570, expelled from there to the dirt anddust collecting bag in which the air is cleaned, and then drawn backfrom the bag to the clean air outlet by the impeller 572.

Another application of the invention is the variation of the ratio ofthe speeds of a motor and a generator. An example of this type ofapplication is the variation of the speeds of the turbine and thecompressor in the turbo-charger on an internal combustion engine in anautomotive vehicle as illustrated in FIG. 9. This can be achieved inpractice by the use of a switched reluctance motor 610 to drive thecompressor 612 and a switched reluctance generator 614 to absorb theenergy of the turbine 616. The speed of the compressor 612 can besynchronised to an integer multiple of the speed of the turbine 616 andto the combination of the ratios of the motor/generator poles so thatthe input power per “stroke” of the generator 614 can be transferreddirectly to the output power per “stroke” of the motor 610. Such avariable ratio turbo-charger has many advantages over a standard unityratio turbo-charger, including improved engine power and efficiency,reduced “turbo” lag, high reliability combined with compact size ofcomponents and robust construction. The arrangement is not expensive tomanufacture and can be linked in to the engine management system. It mayalso provide an opportunity for the vehicle alternator to be removed forbeing redundant.

Many further modifications and variations will suggest themselves tothose versed in the art upon making reference to the foregoingdescription which is given by way of example only and is not intended tolimit the scope of the invention, that being determined by the appendedclaims.

What is claimed:
 1. A switched reluctance motor comprising two or morerotors which are rotated by means of a common power supply, each rotorhaving a plurality of poles and being, associated with a common stator,the stator having a first plurality of poles for driving a first of therotors and a second plurality of poles for driving a second of therotors, wherein the arrangement of rotor poles and stator poles isdifferent for each rotor so that the rotors rotate at different speedswhen the common power supply is applied.
 2. A motor as claimed in claim1, wherein the number of stator poles is the same for each rotor, butthe number of rotor poles is different.
 3. A motor as claimed in claim1, wherein means are provided for causing at least one of the rotors torotate in a direction opposite to the direction of rotation of theremaining rotor or rotors.
 4. A motor as claimed in claim 3, wherein thesaid means comprise magnets which are located in such positions as toprime the rotors, when stationary, for rotation in mutually oppositedirections by locating each rotor pole closer to a predetermined one oftwo adjacent stator poles.
 5. A motor as claimed in claim 1, wherein themotor is housed in a vacuum cleaner.
 6. A motor as claimed in claim 5,wherein one of the rotors is adapted to drive the impeller of the vacuumcleaner.
 7. A motor as claimed in claim 6, wherein a second of therotors is adapted to drive a second impeller of the vacuum cleaner.
 8. Amotor as claimed in claim 6, wherein one of the rotors is adapted todrive a brush bar of the vacuum cleaner.
 9. A motor comprising two ormore rotors rotated by means of a common power supply, each rotor havinga plurality of poles and being associated with a common stator, thestator having a first plurality of poles for driving a first of therotors and a second plurality of poles for driving a second of therotors, wherein the arrangement of rotor poles and stator poles isdifferent for each rotor so that the rotors rotate at different speedswhen the common power supply is applied and one of the rotors forms partof a switched reluctance generator.
 10. A motor as claimed in claim 9,one of the rotors is used to drive a compressor of a turbo charger andthe switched reluctance generator is adapted to absorb energy from theturbine.
 11. A vacuum cleaner comprising a switched reluctance motorhaving two or more rotors rotated by means of a common power supply,each rotor having a plurality of poles and being associated with acommon stator, the stator having a first plurality of poles for drivinga first of the rotors and a second plurality of poles for driving asecond of the rotors, wherein the arrangement of rotor poles and statorpoles is different for each rotor so that the rotors rotate at differentspeeds when the common power supply is applied.
 12. The vacuum cleanerof claim 11, wherein one of the rotors is adapted to drive an impellerof the vacuum cleaner.
 13. The vacuum cleaner of claim 12, wherein asecond of the rotors is adapted to drive a second impeller of the vacuumcleaner.
 14. The vacuum cleaner of claim 11, wherein one of the rotorsis adapted to drive a brush bar of the vacuum cleaner.
 15. The vacuumcleaner of claim 11, wherein a first rotor and a second rotor eachoperate as a switched reluctance motor.
 16. The vacuum cleaner of claim11, wherein a first rotor and a second rotor each operate as a steppermotor.